OFFSET
1,1
COMMENTS
Also, numbers k such that (10^k - 61)/3 is prime.
Terms from Kamada data.
a(19) > 2.5*10^5.
LINKS
EXAMPLE
For k=3, 3*R_3 - 20 = 333 - 20 = 313 which is prime.
MATHEMATICA
Select[Range[0, 250000], PrimeQ[(10^# - 61)/3] &]
PROG
(Magma) [n: n in [2..300] | IsPrime((10^n-61) div 3)]; // Vincenzo Librandi, Apr 10 2015
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Apr 09 2015
STATUS
approved